The prior art teaches the use of test probes in chemical process environments. Some prior art probes use metals as electrodes in a galvanic cell. In other probes an active metal portion of the probe is corroded and its decrease in cross-sectional area is used as an indicator of the corrosivity of its environment. U.S. Pat. Nos. 2,735,754; 2,851,570; 2,987,685; 2,991,439; 2,994,219; 3,004,232; 3,060,721; 3,073,154; 3,108,242, and 3,124,771 show test probes having corrodible metal sensors and electrical resistance measuring systems for their use. The technical advance of most prior art probes resides in the arrangement of probe parts or in the designing of the electrical circuit which detects minute levels of test probe metal loss.
U.S. Pat. No. 4,029,554 discusses oxidative acid buildup in synthetic lubricating oils and uses conventional titration tests for determining acidity. This patent measures electromotive force in a battery formed of dissimilar metals to gauge the degree of synthetic oil degradation.
The prior art corrodible sensor probes do not distinguish between corrosion problems associated with different classes of functional fluids. For example, petroleum lubricants may degrade by an oxidative mechanism, whereas certain synthetic fluids such as organic esters and organophosphates are susceptable to hydrolysis ard acid release.
The acidity developed by hydrolyzable ester functional fluids is conventionally measured by wet analysis methods--viz., acid number by alkali titration. Unfortunately the routine taking of aliquot samples for acid number determination is costly, inconvenient, or hazardous for some industrial applications.
A need exists for a simple remote monitoring system adapted to detect the degradation of modern synthetic hydrolyzable ester functional fluids.